SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Messrs Trommer and Lars April 29 2009 March 2010 Draft Five-Year Review Recommendation Page 3 of 3 Various Sites (TPHg) and benzene, toluene, ethylbenzene and total xylenes (BTEX) in MW16-90, the EHD directed preparation of a feasibility study to remediate the intensely impacted groundwater. The RP's consultant proposed conducting a cone penetrometer testing (CPT) investigation first to better characterize the hydrogeological setting and contaminant distribution before preparing a remedial corrective action plan, which the EHD has approved. As free product has been encountered in the recent past, groundwater is intensely impacted locally, and the plume has migrated onto adjacent site(s), the EHD believes that the people of California, and the adjacent property owners, will benefit from remediation of the core of this plume to accelerate its return to background conditions or water quality objectives. 1717 W. Charter Way, Stockton, CA, Claim Number 4423: In 2008, you concurred with additional site investigation and in 2009 you recommended reinitiation of the site remediation system and consideration of a more aggressive remedial technology; this year you recommend site closure consideration, although the responsible party has not undertaken any remedial activity since cessation of the SVE operation. The recent CPT investigation developed data that in the opinion of the EHD connects the site source area to impacted groundwater near the north margin of the site, which would greatly increase the modeled area of the plume of impacted groundwater. At this time, the EHD is not certain that monitoring well MW-4 is a reliable down-gradient monitoring point, which would mean the plume extent in the down-gradient direction may not be accurately known. While contaminant concentrations in the core area wells have declined since monitoring began in 1999, they have varied in a fairly steady range for the last five years that does not show an obvious decline on the tables. With a mass that has not been estimated, an uncertain lateral extent and a degradation rate that has also not been estimated, the EHD cannot be reasonably sure when site conditions will return to background conditions or achieve water quality objectives, or certify that it will do so in a reasonable time frame. The EHD will give the responsible party an opportunity to address these concerns. Questions or comments should be directed to Nuel Henderson at (209) 468-3436 or to the appropriate case worker as indicated on GeoTracker. Sincerely, Nuel Henderson, PG Engineering Geologist 5-Year Reviews for March 2010 Comment Letter 0410.doc